High shear process for processing naphtha

ABSTRACT

A method and system for processing naphtha, including a high shear mechanical device. In one embodiment, the method comprises forming a dispersion of gas in a naphtha hydrocarbon liquid in a high shear device prior to introduction in a cracking reactor/furnace. In another instance the system for processing naphtha comprises a high shear device for mechanically shearing hydrocarbons.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims the benefitunder 35 U.S.C. §121 of U.S. patent application Ser. No. 12/969,372,filed Dec. 15, 2010, which claims the benefit under 35 U.S.C. §119(e) ofU.S. provisional application No. 61/287,617 filed Dec. 17, 2009,entitled “High Shear Process For Processing Naphtha”, the disclosure ofeach of which is hereby incorporated herein by reference in its entiretyfor all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

1. Field of the Invention

This invention relates to producing lower molecular weight hydrocarbons;specifically it relates to processing naphtha utilizing a high sheardevice.

2. Background of the Invention

Conventionally, the process of cracking hydrocarbons is dependent ontemperature and optionally, the exposure of reactants to catalysts. Theprocess cleaves higher molecular-weight, longer chain, heavyhydrocarbons to form low molecular-weight, short-chain, lighthydrocarbons. These light hydrocarbons may be further refined for liquidfuels and other applications.

Liquid naphtha is obtained in petroleum refineries as one of theintermediate products from the distillation of crude oil and is used asa feedstock for olefin (ethylene and propylene) production. Naphtha isoften cracked by a process commonly referred to as steam cracking wheresteam is injected into the liquid naphtha and briefly (milliseconds)heated to high temperatures (800° C.-900° C.), whereby it is crackedinto lighter components including olefins. Steam cracking of naphthaproduces a mixed stream of light hydrocarbons that includes verydesirable ethylene and propylene components.

However, steam cracking of naphtha is an energy intensive reaction. Forexample, mixing high temperature steam with the naphtha, maintaining thetemperature and reactor residence time represent energy costs associatedwith steam cracking. Additionally, in order to control the light gasproduct composition and cracking efficiency, and minimize coking, theseverity or temperature of the reaction requires control of a narrowrange of operational parameters. Any parameter of the reaction occurringoutside this optimal range results in potential loss of the light gasproducts, revenue, and profit.

There is a need in the industry to reduce energy consumption andincrease the yield of higher value components such as ethylene andpropylene from steam cracking. There is also a need to reduce coking ofsteam cracking furnaces that results in costly downtime, increasedmaintenance, and lost efficiencies.

BRIEF SUMMARY

A system for processing naphtha to form light hydrocarbon liquids andgases is described. The system comprising at least one high shear deviceto mechanically shear the heavier hydrocarbons in naphtha and intimatelydisperse steam uniformly within the naphtha. In certain instances, thesystem comprises a reactant gas stream for forming a reactant gasdispersion in naphtha by high shear processing. The system furthercomprising a cracking reactor/furnace to form mixed hydrocarbonproducts.

A method for processing naphtha to form light hydrocarbon liquids andgases, comprising introducing a naphtha feed to at least one high sheardevice. Further, contacting the naphtha feed with a reactant gas streamfor forming a dispersion of gas in the naphtha. Introducing thedispersion to a cracking reactor to form hydrocarbon products, andseparating the light hydrocarbon products from heavier hydrocarbonproducts. Thus, embodiments described herein comprise a combination offeatures and advantages intended to address various shortcomingsassociated with certain prior devices. The various characteristicsdescribed above, as well as other features, will be readily apparent tothose skilled in the art upon reading the following detailed descriptionof the preferred embodiments, and by referring to the accompanyingdrawings.

These and other embodiments, features and advantages will be apparent inthe following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiment of thepresent invention, reference will now be made to the accompanyingdrawings, wherein:

FIG. 1 is a cross-sectional diagram of a high shear device forprocessing naphtha;

FIG. 2 illustrates a schematic diagram of a high shear naphthaprocessing system;

FIG. 3A illustrates a schematic diagram of a steam cracking furnace withradiant and convection zones;

FIG. 3B illustrates a schematic diagram of a steam cracking furnace witha flash drum.

DETAILED DESCRIPTION

Overview:

The present disclosure provides a system and method for the processingof naphtha and naphtha feedstocks for cracking. The system and methodemploy a high shear mechanical device to provide mechanical shearing ofthe hydrocarbons in naphtha in a controlled environment. In certaininstances, high temperature steam is dispersed into the naphtha bypassing through a high shear device. The high shear dispersion of thesteam, or gaseous water vapor, into the naphtha stream forms adispersion of steam gas bubbles in the liquid naphtha. The dispersion isdirected to a furnace reactor where cracking of the hydrocarbons occurs.The steam and naphtha are processed in the reactor to form a lighthydrocarbon stream, and then the reaction is quenched to stop furtherreactions.

Further, the naphtha is contacted with a multi-gas stream comprising atleast one of a high temperature steam, methane, natural gas, orcombinations thereof. The mixture of naphtha and the multi-gas stream issubjected to a high shear device. The high shear dispersion of thismulti-gas stream into naphtha may be directed to a reactor/furnace. Theproduct of the multi-gas dispersion comprises a light hydrocarbonstream. Under certain conditions, the light hydrocarbon stream comprisesolefins, for instance ethylene or propylene, and acetylenes. Theconditions of the high shear device and the reactor may be controlled toproduce a predetermined product in the light hydrocarbon stream. Incertain instances, a portion of the reacted naphtha products is recycledor introduced to further high shear conditions to produce a selectedlight hydrocarbon stream.

In conventional steam cracking reactors, the contact and reaction timefor the naphtha is often controlled by the gas flow rate through areactor vessel, or furnace which provides contact between the reactantsand/or phases at reaction temperatures and pressures. Without beinglimited by theory a reactor assembly that comprises a high shear deviceallows for intimate mixing of the steam with naphtha thus providing formore precise and uniform temperature control in the cracking furnaceresulting in reduced coking and more control of end product composition.The high shear device of the present invention is also known to createfree radicals under high shear conditions that help propagate thedesired cleavage of short chain length carbon compounds from naphtha.This also allows for higher yields of desirable olefin products from thecracking furnace. A typical analysis for existing naphtha steam crackershave cracked gas compositions as found in Table 1.

TABLE 1 Exemplary Naphtha Cracker Stream Composition Cracked gascomposition wt % Ethylene 24 Propylene 14 Methane 11 Benzene 8 Toluene 8Other ~35 Source: Energy efficient design of the cold train of a steamcracker; Presentation by K. Van Geem+, J. Grootjans+, G. B. Marin235thACS National Meeting, Apr. 10, 2008, New Orleans, LA

Without being limited by theory, the high shear device may also resultin the formation of a narrower molecular-weight distribution ofhydrocarbons continuously from a naphtha feedstock for downstreamapplications. A narrower hydrocarbon distribution improves efficiency ofdownstream distillation and processing. The distribution of hydrocarbonmolecular weights may be considered the distribution about a mean oraverage; in some cases the molecular weight distribution is a Gaussiandistribution about the mean molecular weight or chain length. In furtherinstances, the distribution of hydrocarbon molecular weights may becontrolled.

High Shear Device:

High shear devices (HSD) such as high shear mixers and high shear millsare generally divided into classes based upon their ability to mixfluids. Mixing is the process of reducing the size of inhomogeneousspecies or particles within the fluid. One metric for the degree orthoroughness of mixing is the energy density per unit volume that themixing device generates to disrupt the fluid. The classes aredistinguished based on delivered energy density. There are three classesof industrial mixers having sufficient energy density to createdispersions with particle or bubble sizes in the range of about 0.001 μmto about 50 μm consistently.

Homogenization valve systems are typically classified as high-energydevices. Fluid to be processed is pumped or injected under very highpressure through a narrow-gap valve into a lower pressure environment.The pressure gradients across the valve and the resulting turbulence andcavitations act to break-up and mildly shear any particles, long chainmolecules, bubbles, micelles, or different phases in the fluid. Thesevalve systems are most commonly used in milk homogenization and mayyield average particle size range from about 0.01 μm to about 1 μm. Atthe other end of the spectrum are fluid mixer systems classified as lowenergy devices. These systems usually have paddles or fluid rotors thatturn at high speed in a reservoir of fluid to be processed, which inmany of the more common applications is a food product. These systemsare usually used when average particle, globule, or bubble, sizes ofgreater than 20 microns are acceptable in the processed fluid.

Between low energy, high shear mixers and homogenization valve systems,in terms of the mixing energy density delivered to the fluid, arecolloid mills, which are classified as intermediate energy devices. Thetypical colloid mill configuration includes a conical or disk rotor thatis separated from a complementary, liquid-cooled stator by a closelycontrolled rotor-stator gap, which may be in the range from about 0.25μm to 10.0 mm. Rotors may be driven, for example, by an electric motorvia direct drive, or alternatively, a belt mechanism. Many colloidmills, with proper adjustments, may achieve average particle, or bubble,sizes of about 0.001 μm to about 25 μm in the processed fluid. Thesecapabilities render colloid mills appropriate for a variety ofapplications including, but not limited to: colloidal andoil/water-based dispersion processing. In certain instances, the colloidmills can be applied to processes such as preparation of cosmetics,mayonnaise, silicone/silver amalgam, roofing-tar mixtures, and certainpaint products.

Referring now to FIG. 1, there is presented a schematic diagram of ahigh shear device 200. High shear device 200 comprises at least onerotor-stator combination. The rotor-stator combinations may also beknown as generators 220, 230, 240 or stages without limitation. The highshear device 200 comprises at least two generators, and most preferably,the high shear device comprises at least three generators. The firstgenerator 220 comprises rotor 222 and stator 227. The second generator230 comprises rotor 223, and stator 228; the third generator comprisesrotor 224 and stator 229. For each generator 220, 230, 240 the rotor isrotatably driven by input 250. The generators 220, 230, 240 areconfigured to rotate about axis 260, in rotational direction 265. Stator227 is fixably coupled to the high shear device wall 255.

The generators include gaps between the rotor and the stator. The firstgenerator 220 comprises a first gap 225; the second generator 230comprises a second gap 235; and the third generator 240 comprises athird gap 245. The gaps 225, 235, 245 are between about 0.25 μm (10⁻⁵in) and 10.0 mm (0.4 in) wide. Alternatively, the process comprisesutilization of a high shear device 200 wherein the gaps 225, 235, 245are between about 0.5 mm (0.02 in) and about 2.5 mm (0.1 in). In certaininstances, the gap is maintained at about 1.5 mm (0.06 in).Alternatively, the gaps 225, 235, 245 are different between generators220, 230, 240. In certain instances, the gap 225 for the first generator220 is greater than about the gap 235 for the second generator 230,which is greater than about the gap 245 for the third generator 240.

Additionally, the width of the gaps 225, 235, 245 may comprise a coarse,medium, fine, and super-fine characterization correlating to a decreasein the size of the gaps 225, 235, 245. Rotors 222, 223, and 224 andstators 227, 228, and 229 may be toothed designs. Each generator maycomprise two or more sets of rotor-stator teeth, as known in the art.Rotors 222, 223, and 224 may comprise a number of rotor teethcircumferentially spaced about the circumference of each rotor. Stators227, 228, and 229 may comprise a number of stator teethcircumferentially spaced about the circumference of each stator.

In certain embodiments, the rotor teeth have uniform spacing about thecircumference of each rotor 222, 223, and 224. For example, the distancebetween teeth may be between about 0.5 mm (0.02 in) and about 2.5 mm(0.1 in), alternatively, between about 0.5 mm (0.02 in) and about 1.5 mm(0.06 in). In certain instances, the gap is maintained at about 1.5 mm(0.06 in). In instances, the distance between teeth on each rotor 222,223, and 224 may be different. Without limitation by theory, alteringthe gap in the teeth of the rotor may 222, 223, and 224 pulse the shearrate with each revolution of the rotor.

In certain embodiments, the stator teeth have uniform spacing about thecircumference of each stator 227, 228, and 229. For example, thedistance between teeth may be between about 0.5 mm (0.02 in) and about2.5 mm (0.1 in), alternatively, between about 0.5 mm (0.02 in) and about1.5 mm (0.06 in). In certain instances, the gap is maintained at about1.5 mm (0.06 in). In instances, the distance between teeth on eachstator 227, 228, and 229 may be different. Without limitation by theory,altering the gap in the teeth may configure the stator 227, 228, and 229to pulse the shear rate with each revolution of the rotor.

In embodiments, the inner diameter of the rotor is about 11.8 cm. Inembodiments, the outer diameter of the stator is about 15.4 cm. Infurther embodiments, the rotor and stator may have an outer diameter ofabout 60 mm for the rotor, and about 64 mm for the stator.Alternatively, the rotor and stator may be configured with alternatediameters in order to increase the tip speed and shear pressures, forinstance in a commercial scale device. Without limitation by theory, acommercial scale rotor and stator may have considerably largerdiameters, measure in meters, for instances. In certain embodiments,each of three stages is operated with a super-fine generator, comprisinga gap of between about 0.025 mm and about 3 mm. When a feed stream 205,comprising a dispersible phase and a continuous phase, is sent throughhigh shear device 200, a gap width is predetermined to achieve a desireddispersion.

Feed stream 205 comprises a continuous phase and a dispersible phase forforming dispersion after high shear mixing. In certain instances, thecontinuous phase of feed stream 205 comprises a liquid reactant stream,for instance naphtha. Further, feed stream 205 continuous phase maycomprise any liquid, waxy, or other hydrocarbon residues in the liquidphase. The continuous phase may further comprise a solvent, a carrierliquid, or a reactant carrier, without limitation. The dispersible phaseof feed stream 205 comprises a gas or vapor, such as steam, fordispersion into the continuous phase. Alternatively, the dispersiblephase comprises a gas dissolved in a carrier liquid, for instancemethanol in water, which will not readily mix and/or dissolve in thecontinuous phase. In instances where the feed stream 205 is to bereacted with gases, the dispersible phase comprises: gas bubbles, gasparticles, vapor droplets, globules, micelles, or combinations thereof.The feed stream 205 may include a particulate solid component, forinstance a catalyst, in the dispersible phase. As used herein, thedispersible phase including gases, liquids and solids, comprisesparticles. In certain instances, feed stream 205 comprises aheterogeneous mixture of the dispersible phase in the continuous phase.The heterogeneous mixture may be highly viscous liquid, such as slurriesor pastes. As used herein, heterogeneous mixture encompasses acontinuous phase comprising a naphtha stream with any reactant in thedispersible phase. Without being limited by any particular theory, thefeed stream 205 comprising a heterogeneous mixture has a continuousphase and a dispersible phase prior to or simultaneous with introductionto high shear device 200.

Feed stream 205 introduced to high shear device 200 is pumped throughthe generators 220, 230, 240, such that product dispersion 210 isformed. Product dispersion 210 comprises particles of the dispersiblephase homogeneously distributed through the continuous phase. In eachgenerator, the rotors 222, 223, 224 rotate at high speed relative to thefixed stators 227, 228, 229. The rotation of the rotors forces fluid,such as the feed stream 205, between the outer surface of the rotor 222and the inner surface of the stator 227 creating localized high shearconditions. The gaps 225, 235, 245 generate high shear forces thatprocess the feed stream 205. The high shear forces between the rotor andstator form a more homogeneous dispersion of the dispersible phaseparticles in the continuous phase, to form the product dispersion 210.Additionally, the high shear forces reduce the mean particle size. Eachgenerator 220, 230, 240 of the high shear device 200 has interchangeablerotor-stator combinations for producing a narrow distribution of thedesired particle size. Without limitation by theory, the rotor-statorcombinations are selected to form a desired dispersion and particlesize.

The product dispersion 210 has an average particle size less than about1.5 μm; in certain instances the particles are sub-micron in diameter.In certain instances, the average particle size is in the range fromabout 1.0 μm to about 0.1 μm. Alternatively, the average particle sizeis less than about 400 nm (0.4 μm) and most preferably less than about100 nm (0.1 μm). Preferably, the globules are at least micron sized. Ininstances, the high shear device 200 is configured to producemicron-size steam dispersions in naphtha. In embodiments, the generators220, 230, 240 are configured to produce steam dispersions with averageparticle or globule size ranging from about 1 micron to about 500microns in diameter. In certain embodiments, the globule size is about50 microns in diameter. The globule sizes are be controllable by theamount of shear applied to the fluid and the configuration of thegenerators 220, 230, 240 as described previously.

Tip speed is the velocity (m/sec) associated with the end of one or morerevolving elements that is transmitting energy to the reactants. Tipspeed, for a rotating element, is the circumferential distance traveledby the tip of the rotor per unit of time, and is generally defined bythe equation V (m/sec)=π·D·n, where V is the tip speed, D is thediameter of the rotor, in meters, and n is the rotational speed of therotor, in revolutions per second. Tip speed is thus a function of therotor diameter and the rotation rate. In certain embodiments, alteringthe diameter or the rotational rate may increase the shear rate in highshear device 200.

For colloid mills, typical tip speeds are in excess of 23 m/sec (4500ft/min) and may exceed 40 m/sec (7900 ft/min). For the purpose of thepresent disclosure the term ‘high shear’ refers to mechanicalrotor-stator devices, such as mills or mixers, that are capable of tipspeeds in excess of 1 msec (200 ft/min) and require an externalmechanically driven power device to drive energy into the stream ofproducts to be reacted. A high shear device combines high tip speedswith a very small shear gap to produce significant friction on thematerial being processed. Accordingly, a local pressure in the range ofabout 1000 MPa (about 145,000 psi) to about 1050 MPa (152,300 psi) andelevated temperatures at the tip are produced during operation. Incertain embodiments, the local pressure is at least about 1034 MPa(about 150,000 psi). The local pressure further depends on the tipspeed, fluid viscosity, and the rotor-stator gap during operation.

The shear rate is the tip speed divided by the shear gap width (minimalclearance between the rotor and stator). An approximation of energyinput into the fluid (kW/1/min) may be made by measuring the motorenergy (kW) and fluid output (1/min). In embodiments, the energyexpenditure of a high shear device is greater than 1000 W/m³. Inembodiments, the energy expenditure is in the range of from about 3000W/m³ to about 7500 W/m³.

The high shear device 200 combines high tip speeds with a very smallshear gap to produce significant shear on the material. The amount ofshear is typically dependent on the viscosity of the fluid and the sheargap. The shear rate generated in a high shear device 200 may be greaterthan 20,000 s⁻¹. In embodiments, the shear rate generated is in therange of from 20,000 s⁻¹ to 100,000 s⁻¹. The shear rate generated in HSD40 may be in the greater than 100,000 s⁻¹. In some embodiments, theshear rate is at least 500,000 s⁻¹. In some embodiments, the shear rateis at least 1,000,000 s¹. In some embodiments, the shear rate is atleast 1,600,000 s⁻¹. In embodiments, the shear rate generated by HSD 40is in the range of from 20,000 s⁻¹ to 100,000 s⁻¹. For example, in oneapplication the rotor tip speed is about 40 m/s (7900 ft/min) and theshear gap width is 0.0254 mm (0.001 inch), producing a shear rate of1,600,000 s⁻¹. In another application, the rotor tip speed is about 22.9m/s (4500 ft/min) and the shear gap width is 0.0254 mm (0.001 inch),producing a shear rate of about 901,600 s⁻¹.

The rotor is set to rotate at a speed commensurate with the diameter ofthe rotor and the desired tip speed as described hereinabove. Withoutbeing limited by theory, transport resistance is reduced byincorporation of high shear device 200 such that the dispersion of steamin naphtha is increased and coking of the furnace is reduced.Alternatively, the high shear device 200 comprises a high shear colloidmill that serves to accelerate reactions downstream and in the reactordue to the formation of free radicals created by the high pressures andtemperatures present instantaneously at the tip of the rotating highshear device. Accelerating reactions downstream from the high sheardevice 200 may utilize a single stage or dispersing chamber, in certaininstances. Further, in alternate configurations accelerating reactionsdownstream may include a plurality of inline devices, for instancecomprising at least 2 stages.

Selection of the high shear device 200 is dependent on throughputrequirements and desired particle size in the outlet dispersion 210. Incertain instances, high shear device 200 comprises a DISPAX REACTOR® ofIKA® Works, Inc. Wilmington, N.C. and APV North America, Inc.Wilmington, Mass. Model DR 2000/4, for example, comprises a belt drive,4M generator, PTFE sealing ring, inlet flange 1″ sanitary clamp, outletflange ¾″ sanitary clamp, 2HP power, output speed of 7900 rpm, flowcapacity approximately 300 l/h to approximately 700 l/h (depending ongenerator), a tip speed of from 9.4 m/s to above about 41 m/s (about1850 ft/min to above about 8070 ft/min). Several alternative models areavailable having various inlet/outlet connections, horsepower, tipspeeds, output rpm, and flow rate. In further instances, the high sheardevice 200 comprises any device configured to produce the high shearrate and throughput for forming a product dispersion.

Without wishing to be limited to any particular theory, it is believedthat the degree of high shear mixing in a high shear device issufficient to increase rates of mass transfer. Further, a high sheardevice may produce localized non-ideal conditions that enable formationof free radicals and reactions to occur that would not otherwise beexpected to occur based on Gibbs free energy predictions. Additionally,such reactions would not be expected at low shear mixing parameters.Localized non-ideal conditions are believed to occur within the highshear device resulting in increased temperatures and pressures with themost significant increase believed to be in localized pressures. Theincrease in pressures and temperatures within the high shear device areinstantaneous and localized. In certain instances, the temperature andpressure increases revert to bulk or average system conditions onceexiting the high shear device. In some cases, the high shear-mixingdevice induces cavitation of sufficient intensity to dissociate one ormore of the reactants into free radicals, which may intensify a chemicalreaction or allow a reaction to take place at less stringent conditionsthan might otherwise be required. Cavitation may also increase rates oftransport processes by producing local turbulence and liquidmicrocirculation (acoustic streaming). An overview of the application ofcavitation phenomenon in chemical/physical processing applications isprovided by Gogate et al., “Cavitation: A technology on the horizon,”Current Science 91 (No. 1): 35-46 (2006). The high shear-mixing deviceof certain embodiments of the present system and methods is operatedunder what are believed to be cavitation conditions that might be usefulin reactions for the processing of naphtha and the production of lowermolecular weight compounds.

Alternatively, the application of high shear to a fluid may causetemperature and/or pressure sufficient to mechanically break or cleavemolecular and atomic bonds. Without being limited by theory, themechanical cleavage of these bonds may form free radicals. The freeradical formation may result in localized ionic or free radical attackson other molecular and atomic bonds. The incidence of these ionic and/orfree radical attacks accelerates the rates of reactions in certainhydrocarbon reforming and upgrading reactions. The incidence of ionicand free radicals exposed to hydrocarbons, hydrogen, steam, andoptionally catalysts in the feed stream are believed to push reactionkinetics toward short chain hydrocarbons, such as but not limited toethylene, propylene (propene), and butlyene.

Description of High Shear Process and System for Processing Naphtha:

Referring to FIG. 2, the high shear system 300 (HSS 300) for processingof naphtha comprises a naphtha source 301, a reactor 320, includingreactant feeds 310, and a plurality of processing, separating, andrefining steps to produce a desired light hydrocarbon stream. Thereactor 320 comprises any reactor suitable for the steam cracking ofnaphtha, for instance a furnace reactor. Alternatively, the reactor 320is a furnace. The high shear device 315 provides for improved dispersionof reactants in a dispersible phase into the naphtha as the continuousphase. Further, as described hereinabove, the high shear processingsystem is configured to alter a hydrocarbon distribution in a productstream, such that a narrower distribution of hydrocarbon molecularweights or chain lengths is produced. The distribution of hydrocarbonmolecular weights may be considered the distribution about a mean oraverage; in some cases the molecular weight distribution is a Gaussiandistribution about the mean molecular weight.

Naphtha stream 302 from naphtha source 301 comprises any stream ofhydrocarbon liquids, waxes, residues, mixed hydrocarbons, tars, andnaphtha as understood by one skilled in the art. Naphtha stream 302 isprovided motive force by pump 305. In certain instances, the naphthastream 302 is pressurized by pump 305. Optionally, describedhereinbelow, naphtha stream 302 is subjected to a first high sheardevice 315A to form naphtha stream 303. First high shear device 315A isconfigured to be positioned prior to or after pump 305. Pump 305 isconfigured for either continuous or semi-continuous operation, and maybe any suitable pumping device that is capable of providing greater thanabout 202.65 kPa (2 atm) pressure, preferably greater than about 303.975kPa (3 atm) pressure, to allow controlled flow through HSD 315 andthroughout system 300. Preferably, all contact parts of the pump 305comprise stainless steel, for example, 316 stainless steel. In additionto pump 305, one or more additional pumps (not shown) may be included inthe HSS 300 illustrated in FIG. 2. For example, a booster pump, whichmay be similar to pump 305, may be included between HSD 315 and reactor320 for boosting the pressure, accelerating reactant flow into orthrough reactor 320 to control reaction time. A pump 305 may beimplemented for spent, unused, or incomplete reactant recycle throughoutHSS 300. As another example, a supplemental feed pump, which may besimilar to pump 305, may be included for introducing additionalreactants or catalyst into the components of HSS 300. A Roper Type 1gear pump, Roper Pump Company (Commerce Georgia) Dayton Pressure BoosterPump Model 2P372E, Dayton Electric Co (Niles, Ill.) is an exemplary pumpfor HSS 300. Pump 305 produces HSD feed stream 306.

HSD feed stream 306 comprises the pressurized naphtha stream 302. HSDfeed stream 306 is routed directly or indirectly to HSD 315. HSD feedstream 306 may be any liquid hydrocarbon stream. Further, HSD feedstream 306 may be pretreated by hydrotreating and other means known tothose experienced in the art in order to remove undesirable componentssuch as sulfur and heavy organic compounds by means known to those inthe art, for example as described in U.S. Pat. No. 4,619,757 and U.S.Pat. No. 6,190,533. HSD feed stream 306 is directed to the high sheardevice (HSD) 315. In certain instances, HSD feed stream 306 comprisesheat exchangers. HSD feed stream 306 may be heated or cooled any methodknown to one skilled in the art. The use of external heating and/orcooling heat transfer devices for changing the temperature of HSD feedstream 306 is also contemplated. Some non-limiting examples of such heatexchangers include shell, tube, plate, and coil heat exchangers, as areknown in the art.

HSD feed stream 306 may also be in fluid communication with a gas stream310. Gas stream 310 comprises a dispersible phase stream. In instanceswhere HSS 300 comprises a steam cracker for naphtha, gas stream 310comprises steam or water vapor. Alternatively, the dispersible phase maycomprise mixtures of steam with hydrogen, methane, natural gas, andother gaseous components, such as water vapor, comprising gas stream310. Gas stream 310 is fluidly connected to a supplemental gas stream312, and in instances, gas stream 310 comprises the components ofsupplemental gas stream 312. Injecting gas stream 310 forms aheterogeneous mixture of the dispersible phase, gas stream 310, and thecontinuous phase, naphtha stream 302 in HSD feed stream 306. HSD feedstream 306 is introduced into HSD 315.

Supplemental gas stream 312 adds additional gas reactants and/orenhancers to gas stream 310. Supplemental gas stream 312 may comprise aplurality of gaseous reactants, for instance, steam, hydrogen, and/ormethane. It can be envisioned that supplemental gas stream 312 providesparticulates to gas stream 310, for instance catalyst fines.Alternatively, supplemental gas stream 312 comprises a recycle streaminlet for off-gases, which are conventionally flared. Gas stream 310,comprising supplemental gas stream 312, is injected into HSD stream 306.Alternatively, gas stream 310 may be injected into HSD 315 directly.

High shear device (HSD) 315, as any described hereinabove. Inembodiments, HSD 315 comprises a plurality of high shear generators toform HSD dispersion 318. HSD 315 comprises at least a high shear, threestage dispersing device configured with three rotors in combination withstators, aligned in series. For example, disperser IKA® model DR 2000/4,may be used as HSD 315, to create the dispersion of dispersible gas inthe naphtha. The rotor-stator sets may be configured as illustrated forexample in FIG. 1. In instances, HSD feed stream 306, gas stream 310,and supplemental gas stream 312, pass through the stages of HSD 315. TheHSD feed stream 306, gas stream 310, and supplemental gas stream 312 aretherein subjected to shear to form HSD dispersion 318.

The rotors of HSD 315 may be set to rotate at a speed commensurate withthe diameter of the rotor and the desired tip speed. As described above,the high shear device (e.g., colloid mill or toothed rotor) has either afixed clearance between the stator and rotor or has adjustableclearance. The mixing and shear in HSD 315 is increased at arotor-stator by decreasing the rotor-stator gaps, or increasing therotational rate of the rotor, and vice-versa. HSD 315 delivers at least300 L/h at a tip speed of at least 4500 ft/min, and which may exceed7900 ft/min (40 m/s). Although measurement of instantaneous temperatureand pressure at the tip of a rotating shear unit or revolving element inHSD 315 is difficult, it is estimated that the localized temperatureseen by the intimately mixed reactants is in excess of 500° C. and atpressures in excess of 500 kg/cm² under cavitation conditions. The highshear mixing results in dispersion of micron or submicron-sized gasbubbles in a continuous liquid phase comprising naphtha, as HSDdispersion 318. Further, the HSD 315 may comprise any components andoperating conditions configurable and operable to achieve a desiredshear between the rotor-stators.

In HSD 315, the rotors and stators of the stages may havecircumferentially spaced first stage rotor teeth and stator teeth,respectively. In certain configurations, the rotor-stator gap decreasesstepwise from stage to stage. Alternatively, the rotor-stator gap isconfigured to be constant from stage to stage. Further, HSD 315 maycomprise a heat exchanger. In non-limiting examples, a heat exchangerfor HSD 315 comprises a conduit for directing a thermal fluid in contactwith a thermally conductive portion of the device. More specifically,HSD 315 comprises a PTFE seal that may be cooled using any suitabletechnique that is known in the art. For example, gas stream 310 and/orsupplemental gas stream 312 used to cool the seal and in so doing bepreheated as desired prior to entering HSD feed stream 306.

HSD 315 is configured to flow the HSD feed stream 306 through therotor-stator stages to form HSD dispersion 318. In instances, HSD feedstream 306 enters a first stage rotor-stator combination and issubjected to the mixing and shear of the first stage. The coarsedispersion exiting the first stage enters the second rotor-stator stage,and is subjected to increased mixing and shear. The further reduced, orintermediate, bubble-size dispersion emerging from the second stageenters the third stage rotor-stator combination. The third stagerotor-stator is configured to produce the comparatively highest mixingand shear conditions. Configured thusly, HSD 315 sequentially increasesthe mixing and shear conditions at each stage. Alternatively, the shearrate is substantially constant along the direction of the flow, with theshear rate in each stage being substantially the same. In anotherconfiguration, the shear rate in the first rotor-stator stage is greaterthan the shear rate in subsequent stage(s).

The HSD feed stream 306 is subjected to the high shear conditions in theHSD 315. The gas stream 310 and naphtha stream 302 of HSD stream 306 aremixed within HSD 315, which serves to create a fine dispersion of thegas in the naphtha. HSD 315 serves to intimately mix the gas and naphthaunder high shear conditions. In HSD 315, the gas and naphtha are highlydispersed such that nanobubbles, submicron-sized bubbles, and/ormicrobubbles of gas are formed for dissolution into solution andenhancement of reactant mixing. The resultant dispersion has an averagebubble size less than about 1.5 μm. Accordingly, the dispersion exitingHSD 315 comprises micron and/or submicron-sized gas bubbles. In someembodiments, the resultant dispersion has an average bubble size lessthan 1 μm. In some embodiments, the mean bubble size is in the range ofabout 0.4 μm to about 1.5 μm. In some embodiments, the mean bubble sizeis less than about 400 nm, and may be about 100 nm in some cases. Bubblesize is dependent on local pressures and temperatures and may beestimated by ideal gas laws. In embodiments, the dispersion is able toremain dispersed at atmospheric pressure for at least about 15 minutes.

HDS dispersion 318 feeds reactor 320 for producing a mixed hydrocarbonproduct stream 322, hereinafter MHCP 322. Reactor 320 is any reactorsuitable for high temperature, low pressure naphtha cracking.Alternatively, reactor 320 comprises a furnace reactor, coupled to afurnace or heater 321. Further, reactor 320 may comprise a fluidized bedreactor, slurry reactor, fixed bed reactor, trickle bed reactor, bubblecolumn, or the like in thermal communication with the reactor 320. Ininstances wherein a catalyst is implemented in the reactor 320 toincrease the rate of reaction, drive the reaction to a selected product,or to alter the conditions of the reaction, the reactor 320 may includeadditional components without limitation. Further, the reactor 320 mayinclude one or more of the following components: convection heatingzone, radiant high temperature heating zone, heat exchangers, agitators,mixers, reaction condition measurement instrumentation, reactionregulators, pressure measurement instrumentation, temperaturemeasurement instrumentation, one or more injection points, and levelregulator (not shown), as are known in the art of reaction vesseldesign. For example, a stirring system may include a motor driven mixer.A heating and/or cooling apparatus may comprise, for example, a heatexchanger.

Reactor 320 operates such that naphtha reaches temperatures ranging fromabout 200° C. to about 1100° C. depending on location within thereactor, location with the furnace, and low pressures ranging from about101.3 kPa to about 202.6 KPa (1 atm to 2 atm) of absolute pressure. Ingeneral for paraffinic feedstocks, temperatures above about 400° C.result in a shift from cracking at the center of the molecule to the endof the molecule leading to larger quantities olefin products. Shortresidence times also results in less coking of the reactor and moreolefin production. Cracked products typically exit the reactor furnaceat a temperature between about 800° C. and about 900° C. Withoutlimitation by theory, the formation of olefins is favored by lowerpressures. In instances, steam is added to the naphtha to decrease thepartial pressure of the hydrocarbons and to minimize coke formation. Insome configurations, the pressure in reactor 320 is less than about202.25 KPa (2 atm), alternatively, less than about 101.3 kPa (1 atm). Incertain instances, it may be preferable to maintain the minimum gaspressure necessary to transport the HSD dispersion 318 through thereactor 320 for a given residence time. Without limitation by theory,the gas pressure is maintained between about 10 psig and about 200 psig,and preferably between about 30 psig and about 100 psig. The residencetime in the reactor 320 is kept as low as possible, preferably less thanabout 100 milliseconds. In the cracking process, the splitting ofhydrocarbons in the absence of any chain terminating element ormolecule, such as hydrogen without limitation, results in the formationof double bonds that produce desirable light hydrocarbon products suchas ethylene and propylene.

In certain instances, reactor 320 comprises a furnace tube 321 formoving the HSD dispersion 318 through multiple zones, portions, orsections of the reactor 320. Referring now to FIG. 3A, in certaininstances, HSD dispersion 318 enters reactor 320 at a convection section340. Convection section 340 is configured to heat HSD dispersion to atemperature of between about 200° C. and about 600° C., and in certaininstances to between about 200° C. and about 350° C. As the HSDdispersion 318 is heated, it forms heated dispersion 342. In instances,heated dispersion 342 is routed to a radiant section 344 of the reactor320 either directly or indirectly. In certain configurations, heateddispersion 342 is routed outside of reactor for thermal exchange 343 toproduce steam or supplemental steam. Thermal exchange 343 may compriseany apparatus understood by a skilled artisan as suitable fortransferring thermal energy from one a fluid to another. In certaininstances, thermal exchange is a heat exchanger, such as a counterflowheat exchanger or a cross-flow heat exchanger.

Alternatively, heated dispersion 342 is directly routed to a radiantsection 344 of the reactor 320. Radiant section 344 of reactor 320increases the temperature of the heated dispersion to a temperaturebetween about 600° C. to about 1100° C. Without limitation by theory,the radiant section 344 comprises the cracking reactions in reactor 320to form MHCP stream 322. In instances, the residence time, temperatureand pressure in the reactor 320 are dependent on the HSD dispersion 318,the components of the naphtha stream 302, and the desired composition ofthe MHCP stream 322. In further instances, the residence time,temperature, and pressure are dependent on the composition of the gasstream 310.

In alternate configurations, heated dispersion 342 is directed to anycomponent for removing heavy hydrocarbon fractions that may fouloperation of reactor 320. Referring now to FIG. 3B, the reactor 320comprises a furnace tube 321 for moving the HSD dispersion 318 throughmultiple zones, portions, or sections of the reactor 320. HSD dispersion318 enters reactor 320 at a convection section 340, and is routed to aseparator 360 by feed 343. In instances, the separator 360 comprises aflash drum. Without limitation by theory, a flash drum may be anevaporator, a flash reactor, or any other vapor-liquid separator knownto a skilled artisan. In instances, the separator 360 is configured tooperate at a temperature of about 200° C. to about 600° C., and incertain instances, operate at a temperature of about 450° C. Additionalsteam 363 may be introduced into separator 360 for enhancing the steamconcentration therein, initiating cracking reactions, or improving thesteam to naphtha ratio in the dispersion. The separator 360 isconfigurable to separate heavy molecular weight hydrocarbons, or heavyfractions, from light molecular weight hydrocarbon, or light fractions.The separator 360 forms a return stream 372 to the reactor 320,comprising the light hydrocarbon fractions. In certain configurations,return stream 372 is routed additionally through a heat exchanger (notshown) to produce steam or supplemental steam. The heat exchanger maycomprise any apparatus understood by a skilled artisan as suitable fortransferring thermal energy from one a fluid to another. In certaininstances, the heat exchanger is a counterflow heat exchanger or across-flow heat exchanger. In instances, the return stream 372 may bereturned to the convection section 340 for heating or directly to theradiant section 344 for cracking. Radiant section 344 of reactor 320increases the temperature to a temperature between about 600° C. toabout 1100° C. Without limitation by theory, the radiant section 344comprises the cracking reactions in reactor 320 to form MHCP stream 322.In instances, residence time, temperature and pressure in the reactor320 are dependent on the HSD dispersion 318, the components of the gasstream 310, the components of the naphtha stream 302, and the desiredcomposition of the MHCP stream 322.

Alternatively, separator 360 produces a crude light fraction stream 361that is fed to condenser 370. Condenser 370 functions as a streamscrubber and removes any remaining heavy fraction hydrocarbons from thereturn stream 372. The heavy hydrocarbon fraction is returned toseparator as return stream 362. In further instances, the separator 360forms heavy fraction stream 364 for routing to other downstreamprocesses.

In certain instances, steam 363 may be in fluid communication withseparator 360. The separator produces a light fraction stream 361 thatis fed to condenser 370. Condenser 370 functions as a stream scrubberand removes any remaining heavy fraction hydrocarbons from the reactorreturn stream 372 as a return stream 362. In further instances, theseparator 360 forms heavy fraction stream 364 for routing to additionalprocesses, or in certain instances as a burn stream.

Referring again to FIG. 2, in some embodiments of the process, thetransport resistance is reduced and uniformity of the reactants in HSDdispersion 318 is increased by operation of HSD 315 such that steam usecan be reduced by about >5% without increased furnace coking, and thepercentage of desirable olefins exiting the reactor/furnace is increasedby about >5%. In instances, MHCP stream 322 comprises hydrocarbons withgreater olefin content than that without the use of HSD 315. Further, ininstances, MHCP stream 322 comprises olefin content greater than about40%. In certain instances, MHCP stream 322 comprises olefin contentgreater than 45%. MHCP stream 322 comprising a distribution of lighterhydrocarbons is directed to a quench 324 to stop the reactions andprevent the reverse reactions or further reactions. In instances, quench324 reduces the temperature of MHCP stream 322 from between about 800°C. to 900° C. to between about 200° C. and about 400° C., and in certainconfigurations to about 300° C. For preventing the formation of carbon,coke, and other undesirable hydrocarbon compounds, extremely rapidcooling or quenching, typically in 1 to 100 milliseconds, isadvantageous. Further, the quench 324 in HSS 300 may be achieved byspraying water, oil, solvent or other compatible liquid into a reactorquench chamber. Alternatively, the quench 324 comprises a conduitthrough or into water; or expanded in a kinetic energy quench such as aJoule Thompson expander, choke nozzle or turbo expander. Quench 324 incertain instances comprises introducing a fluid, such as a heavyhydrocarbon, an inorganic liquid, acetylene solvent, water or steam, oranother fluid to MHCP stream 322. Quench 324 comprises the liquidintroduction in sufficient quantity to abate ongoing reactions in MHCPstream 322. Further, quench 324 is introduced to MHCP stream 322 as ameans to maximize olefin concentration by ceasing further reactions andconversions within MHCP stream 322. Quenching MHCP stream 322 forms aquenched stream 326. Quenched stream 326 is routed to further processing350 for downstream products and applications.

Multiple High Shear Mixing Devices:

In certain instances, two or more high shear devices are used to furtherenhance the reaction in HSS 300. Their operation may be in either batchor continuous mode. In instances, the HSS 300 comprises configurationand process flow changes to derive benefit for the implementation ofmultiple high shear device arrangements. In instances, the high sheardevices may be used as a pretreatment device to prepare the naphthafeedstock prior to cracking as described in US Pat. App. No. US2009/0000989 to Hassan et al.

The application of enhanced mixing, free radical generation andmechanical shearing of the hydrocarbon components in naphtha by a highshear device potentially permits more effective hydrocracking of naphthastreams with better selectivity of end product components and reducedfouling of system components. In some embodiments, the enhanced mixingpotentiates a reduction in steam, an associated energy consumption toachieve cracking of naphtha. In some embodiments, the high shear mixingdevice is incorporated into an established process, thereby enabling anincrease in production (i.e., greater throughput). In contrast to somemethods that attempt to increase the degree of hydrocracking by simplyincreasing the reactor operating temperature, or residence time, thesuperior dispersion free radical generation and contact provided byexternal high shear mixing may allow, in many cases, a decrease inoverall operating temperature, residence time, and/or efficiency, whilemaintaining, or even increasing, throughput.

While the preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described and the examples provided herein are exemplaryonly, and are not intended to be limiting. Many variations andmodifications of the invention disclosed herein are possible and arewithin the scope of the invention. Accordingly, the scope of protectionis not limited by the description set out above, but is only limited bythe claims that follow, that scope including all equivalents of thesubject matter of the claims.

We claim:
 1. A high shear system for processing of naphtha, the systemcomprising; at least one high shear device comprising an inlet and atleast one rotor-stator combination configured for producing a shear rateof at least 20,000 s⁻¹, wherein the inlet is configured for theintroduction of a high shear feed comprising naphtha and a dispersiblephase, and wherein the at least one high shear device is configured toproduce a dispersion; a pump positioned upstream of the at least onehigh shear device, the pump configured to introduce the high shear feedinto the at least one high shear device; and a cracking reactorconfigured to crack at least a portion of the components of thedispersion, thus producing a cracked product comprising lighterhydrocarbon compounds.
 2. The system of claim 1 further comprising asupplemental gas line in fluid communication with the inlet.
 3. Thesystem of claim 2, wherein the dispersible phase comprises at least onecomponent selected from the group consisting of steam, hydrogen,methane, and natural gas.
 4. The system of claim 1, wherein a convectionsection of the cracking reactor is configured to produce a mixedhydrocarbon stream.
 5. The system of claim 4 further comprising aseparator configured to separate a light hydrocarbon stream from themixed hydrocarbon stream.
 6. The system of claim 5, wherein theseparator comprises a flash drum.
 7. The system of claim 1, wherein theat least one high shear device is configured to produce a dispersionhaving an average gas bubble diameter of less than about 50 μm.
 8. Thesystem of claim 1 further comprising at least a second high sheardevice, wherein the second high shear device is positioned upstream ofthe pump.
 9. The system of claim 1, wherein the high shear device isconfigured to mechanically homogenize the naphtha stream.
 10. The systemof claim 1 further comprising at least one heat exchanger, wherein theat least one heat exchanger is configured to preheat the high shearfeed.
 11. The system of claim 1, wherein the at least one high sheardevice comprises at least two rotor-stator combinations.
 12. The systemof claim 1, wherein the cracking reactor comprises a furnace reactor.13. The system of claim 12, wherein the furnace reactor is a steamcracking furnace comprising convection and radiant zones.
 14. The systemof claim 13 further comprising a separator fluidly connected with theconvection zone of the steam cracking furnace and configured to separatea feed extracted from the convection zone into a heavy hydrocarbonfraction and a light hydrocarbon fraction, and introduce the lighthydrocarbon fraction back into the steam cracking furnace.
 15. Thesystem of claim 13, wherein the dispersible phase comprises steam, andwherein the steam cracking furnace further comprises a thermal exchangesection configured to route at least a portion of the dispersion outsidethe steam cracking furnace, whereby steam can be produced via thermalexchange therewith.
 16. The system of claim 1, wherein the crackingreactor is operable at a temperature in the range of from about 200° C.to about 1100° C., and a pressure in the range of from about 1 atm toabout 2 atm.
 17. The system of claim 1 further comprising a quenchdevice fluidly connected with the cracking reactor, and configured toquench the cracked product.
 18. The system of claim 16, wherein thequench device is configured to provide quenching in from 1 ms to 100 ms.19. The system of claim 16, wherein the quench device is configured toreduce the temperature of the cracked product from a temperature in therange of from about 600° C. to about 1100° C., to a temperature in therange of from about 200° C. to about 400° C.
 20. The system of claim 1,wherein the at least one high shear device is configured to produce adispersion comprising primarily micron or submicron-sized steamparticles dispersed in naphtha.